User blog comment:Sweetangel823/Single List/@comment-30795583-20160810173420/@comment-26432224-20160810174207

^ Look at Milly's blog history. You'll find it there. And it's not "to earn a solo" but to have a good reason. For example being a pushed member (like Acchan, Sayaka, Takamina, Miyaya who all are constantly in the senbatsu/front members of their generation/team songs) or having a good ranking in the senbatsu sousenkyo ("general elections" in the anime subs).